Re: [PATCH] PCI: tegra: Fix shiftTooManyBitsSigned warning for Tegra194

[Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>]

On Thu, Jun 24, 2021 at 06:01:50PM -0500, Bjorn Helgaas wrote:
> On Fri, Jun 18, 2021 at 06:04:28PM -0500, Bjorn Helgaas wrote:
> > On Fri, Jun 18, 2021 at 05:02:19PM +0100, Jon Hunter wrote:
> > > The cppcheck tool issues the following warning for the Tegra194 PCIe
> > > driver ...
> > > 
> > >  $ cppcheck --enable=all drivers/pci/controller/dwc/pcie-tegra194.c
> > >  Checking drivers/pci/controller/dwc/pcie-tegra194.c ...
> > > 
> > >  drivers/pci/controller/dwc/pcie-tegra194.c:1829:23: portability:
> > > 	Shifting signed 32-bit value by 31 bits is
> > > 	implementation-defined behaviour. See condition at line 1826.
> > > 	[shiftTooManyBitsSigned]
> > > 
> > >   appl_writel(pcie, (1 << irq), APPL_MSI_CTRL_1);
> > >                       ^
> > > The above warning occurs because the '1' is treated as a signed type
> > > and so fix this by using the 'BIT' macro to ensure that this is defined
> > > as a unsigned type.
> > 
> > The subject and commit log should describe the problem we're fixing.
> > The *warning* is not the problem; the problem is the undefined
> > behavior.

I updated the commit log accordingly but I did not change the
subject :-/

> > I'll fix this up, no need to repost for this.
> 
> I merged this from Lorenzo's branch, but I updated the commit log like
> this because the undefined behavior is the real problem:
> 
>     PCI: tegra194: Fix tegra_pcie_ep_raise_msi_irq() ill-defined shift

Yep, I forgot to update the subject, thanks for doing that.

Lorenzo

> 
>     tegra_pcie_ep_raise_msi_irq() shifted a signed 32-bit value left by 31
>     bits.  The behavior of this is implementation-defined.
> 
>     Replace the shift by BIT(), which is well-defined.
> 
>     Found by cppcheck:
> 
>       $ cppcheck --enable=all drivers/pci/controller/dwc/pcie-tegra194.c
>       Checking drivers/pci/controller/dwc/pcie-tegra194.c ...
> 
>       drivers/pci/controller/dwc/pcie-tegra194.c:1829:23: portability: Shifting signed 32-bit value by 31 bits is implementation-defined behaviour. See condition at line 1826.  [shiftTooManyBitsSigned]
> 
>       appl_writel(pcie, (1 << irq), APPL_MSI_CTRL_1);
>                          ^
> 
>     [bhelgaas: commit log]
>     Link: https://lore.kernel.org/r/20210618160219.303092-1-jonathanh@nvidia.com
>     Fixes: c57247f940e8 ("PCI: tegra: Add support for PCIe endpoint mode in Tegra194")
>     Signed-off-by: Jon Hunter <jonathanh@nvidia.com>
>     Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
>     Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
> 
> > > Fixes: c57247f940e8 PCI: tegra: Add support for PCIe endpoint mode in Tegra194
> > > Signed-off-by: Jon Hunter <jonathanh@nvidia.com>
> > > ---
> > >  drivers/pci/controller/dwc/pcie-tegra194.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > 
> > > diff --git a/drivers/pci/controller/dwc/pcie-tegra194.c b/drivers/pci/controller/dwc/pcie-tegra194.c
> > > index 8fc08336f76e..3c1feeab104f 100644
> > > --- a/drivers/pci/controller/dwc/pcie-tegra194.c
> > > +++ b/drivers/pci/controller/dwc/pcie-tegra194.c
> > > @@ -1826,7 +1826,7 @@ static int tegra_pcie_ep_raise_msi_irq(struct tegra_pcie_dw *pcie, u16 irq)
> > >  	if (unlikely(irq > 31))
> > >  		return -EINVAL;
> > >  
> > > -	appl_writel(pcie, (1 << irq), APPL_MSI_CTRL_1);
> > > +	appl_writel(pcie, BIT(irq), APPL_MSI_CTRL_1);
> > >  
> > >  	return 0;
> > >  }
> > > -- 
> > > 2.25.1
> > >